Claim

CT scans increase your risk of cancer by 35%.

Verdict

False

There is no scientific evidence to support the claim that CT scans increase the risk of cancer.

Origin

CT or computerized tomography helps visualize internal body organs such as the brain, kidney, spleen, liver. CT uses ionizing radiation at a higher dose than standard x-rays. The widespread use of CT scans has raised concerns that CT scans may increase the risk of solid organ cancer or leukemia. Theoretically any risk would be highest in children who are more sensitive to radiation and have a longer life expectancy than their adult counterparts (2).

A low dose CT scan of the chest exposes patients to 1.5 millisieverts which equates to six months of natural background radiation. A regular dose CT scan of the chest exposes patients to 7 millisieverts, which equates to two years of natural background radiation. The average person living in the USA is exposed to about 3 millisieverts of radiation exposure from naturally occurring radioactive materials such as radon.

An Australian research group took on finding the answer to the question about the risk of cancer with CT imaging (1). The Australian Medicare system has electronic health records for all Australians. The system operates on a fee for service, which means that any CT scans carried out is recorded within the database. The researchers identified 10.9 million people aged between zero and 19 years in 1985 and followed their health records through to the year 2007.

The study found that a diagnosis of cancer was statistically more likely in study participants who were exposed to CT radiation. As expected the risk was greater at younger ages and with each additional scan. The incidence of cancer did increase by 35% in people exposed to CT scans as compared to those did not have CT scans.

The problem with results of a study is that it only tells of an ‘association’ between CT scans and cancer and not ‘causation’. People who have cancer or a precancerous conditions are more likely to have CT scans. This explains the ‘association’ between CT scans and cancer. Proving causation or that CT scans causes cancer is entirely different. This study did not prove that CT scans cause cancer. In fact this study design could never prove that CT scans cause cancer.

Conclusion: There is no basis for the claim that CT scans cause cancer. Any risk-benefit analysis of having a CT scan has to take into account the fact that the benefits of having a diagnostic CT scan in patients with signs or symptoms of significant disease would outweigh any theoretical risk of developing cancer from the CT scan itself. Moreover, modern CT scanners use less radiation than the older scans such as the ones used in the Australian study between the years of 1985 and 2007.

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